A long-wavelength and color-changed cellulose-based fluorescent sensor for Al3+ and its applications in detection and fluorescence imaging.

A cellulose ester-based fluorescent derivative (EC-HNCA) was successfully synthesized via the reaction between 3-hydroxy-4-(2-hydroxy-4-sulfo-1-naphthylazo)naphthalene-2-carboxylic acid and ethyl cellulose. The structural variations before and after the synthesis were systematically characterized by proton nuclear magnetic resonance (1H NMR), fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) techniques. EC-HNCA showed no intrinsic fluorescence in solution under 365 nm UV light, while strong pink fluorescence was distinctly observed upon the introduction of Al3+, revealing its excellent selectivity toward Al3+. Moreover, a favorable linear correlation was established between the peak fluoresence intensity (610 nm) and Al3+ concentration within the range of 0-6.5 × 10-6 mol/L, with regression equation y = 225,461×-42,707 (R2 = 0.9910). The limit of detection (LOD) was calculated to be 7.6 nM. The EC-HNCA + Al3+ complex displayed diverse light-emitting colors in different solvent media. Furthermore, the EC-HNCA + Al3+ system was applied to fluorescence imaging of vascular tissues in watermelon rind, and clear fluorescent imaging results were obtained. The detection solution containing EC-HNCA emitted prominent pink fluorescence after adding Al3+ (0.5 × 10-5 mol/L), which could be utilized for the determination of Al3+ in fresh white radish, garlic, Moso bamboo shoots, and Chinese cabbage. Consequently, EC-HNCA held great potential for further applications in plant tissue fluorescence imaging and detection of Al3+.